1. Field of the Invention
The present invention relates to a rolling oil having high lubricating properties and high mill cleanability, that is, a cold-rolling oil for steel plates, which excels in lubricating and annealing properties.
2. Brief Description of the Prior Art
Cold-rolling oils used for thin steel plates are generally broken down into two types, one based on animal and vegetable oils and fats (such as tallow and lard, soybean oil, colza oil, palm oil and coconut oil) and the other on mineral oils. Recent demands for energy saving and improvements in productivity lead to higher speed rolling, higher reduction-ratio rolling and mill clean rolling. The rolling oils based on animal and vegetable oils and fats are suitable for high-load and -speed rolling. However, when cold-rolled steel plates are directly annealed without degreasing oily deposits thereon, it is likely that they may be contaminated on their surfaces in the annealing step. That is, such as those described above are suitable in view of lubricating properties, but are unsuitable in view of mill cleanability.
When cold rolling is carried out with the rolling oils based on mineral oils, excellent mill cleanability is achievable, since cold-rolled thin steel plates can be directly annealed without any surface contamination. However, rolling oils based on mineral oils lack in high-load and -speed rolling properties.
In use, oilness improvers such as animal and vegetable oils and fats, fatty acids (capric, lauric, myristic, stearic, oleic and linolenic acids) or esters (synthetic esters such as monoesters, diesters or polyol esters wherein the alcoholic components are trimethylolpropane, pentaerythritol and 2-ethylhexyl alcohol) as described in "Oil Chemistry", No. 73-11, pages 695-706 are generally added to the rolling oils based on mineral oils so as to enhance their lubricating properties. However, the amount of such improvers added is limited to a narrow range of the required minimum limit so as to retain mill cleanability. As mentioned above, various investigations have been made of cold-rolling oils capable of satisfying high lubricating properties and high mill cleanability at the same time (see for instance Japanese Patent Laid-Open Publication Nos. 56-135600 and 59-80498). However, there are still no oils having both properties in a well-balanced state and at a higher level.